Busway electrical distribution systems are well known in the art of electrical distribution. Referring to FIG. 1, busway systems are comprised of a number of field-assembled sections 100 each including a number of individually insulated generally flat electrical conductors or busbars 101A-101D stacked one upon another in close thermal contact as shown and enclosed within an enclosure or housing 110 that provides protection and support for the busbars. Each housing includes a duct top 111 and a duct bottom (not shown) which cover the flat surfaces of the bus bars 101 and two duct sides (e.g., side 113), which cover the edges of the busbars. The duct tops and bottoms 111 can be made of electrically conductive material such as aluminum or copper for carrying the system ground current. The duct sides 113 are generally made of steel formed to provide strength to the housing. The housing structure 110 also performs a heat-sinking or heat-dissipation function. The housing 110 is generally held together by screws and nuts, rivets, or other similar methods.
The width of the housing 110 is determined by the width of the busbars 101 and the number of busbar stacks enclosed within the housing 110. The busbars 101 may be sized to carry at least 100 amperes of current, often thousands of amperes of current. During a short circuit, magnetic forces around the busbars tend to push the busbars 101 away from each other, thereby causing the tops and bottoms 111 to bulge. High short circuits can cause the housing 110 to be pulled apart. To prevent or limit short circuit damage, surge clamps (e.g., 121A and 121B) may be placed across the duct tops and bottoms at each end of the busway section 100 and at predetermined intervals between the ends.
The busway section 100 includes an end portion 120 at which the busbars 101 are curved so as to flare apart, allowing for connection to another busway section.
In such a busway system 100, it is known to insulate the busbars 101 using a polyester film. One such suitable polyester film is the MYLAR™ brand polyester film made by DuPont. In one known arrangement, polyester film is formed into U-shaped sheaths. A first sheath fits around a busbar leaving one edge of the busbar exposed. Two such sheaths are placed over a busbar from opposite sides of the busbar so as to fully enclose and insulate the busbar. The flat portions of the busbar are therefore covered by two layers of polyester film corresponding to the two sheaths.
Where the busbar bends or curves, it has been necessary to cut the side portions of the sheaths in the region of the bend to allow the sheaths to follow the bend. The exposed portions of the busbar are then insulated with insulating tape. In a busway having busbars insulated in this fashion, overlapping layers of polyester film and tape result in gapping between the busbars. For example, assuming a tape thickness of 6 mils, with 50% overlap, an air gap of 24 mils will be present between the busbars of each phase of a busway over a 10 foot length, for example. Air gapping between the busbars significantly and undesirably increases the thermal resistance of the busway and interferes with effective heat dissipation and busway efficiency.